Patent GB-440928-A (GB)
Title: Method and apparatus for producing one-piece multifocal opthalmic lenses
IPC: B24B13/00
Filed: 1935-05-01
Abstract: 440,928. Grinding &c. lenses. HUBBELL, D. D., 82, North High Street, Columbus, Ohio, U.S.A. May 1, 1935, No. 13035. Convention date, July 27, 1934. [Class 60] A machine for grinding one-piece bifocal lenses with non-circular reading portions, and stated to be applicable also to the production of multifocal lenses, comprises a base 1 carrying a standard 5 having at its upper end a yoke 7, in the arms 8 of which are formed bearings 9 to receive a pin 10, turnable and slidable in the bearings. On the pin 10 is mounted, by means of a housing 12, a block 11, adjustable axially with the pin 10 by a screw 13 and a nut 14, a spring 18 also being provided to prevent play, and the forward part of the block 11 is split and provided with a screw 24 adjustably to secure therein a pin 21. The pin 21 at its outer end carries a yoke 26 formed with bearings 29, 30 for a spindle 31, which is adjustable axially by a screwed sleeve 32 and ball bearing 33, and the yoke also carries a handle 35 and a pin 36 for mounting weights if required. On the spindle is splined a pulley 37, driven by a belt 48 from a pulley 47 driven by an electric motor 44 carried by a member 43 adjustably clamped on a rod 40 carried by the block 11 ; the member 43 may be adjusted angularly on the rod and also, to tighten the belt, along the rod, and the spindle 31, motor 44 and drive may be swung upwardly with the pin 10 without disturbing the drive. The lower end of the spindle 31 carries a tool 49 comprising a bifurcated stem 50 with a block 52 therein, the block and the stem having spherical ends 53, 57 loosely engaging sockets in a disc 55, which carries the operative portion 59 of the tool, this portion being of brass &c, for grinding, and of pitch &e. for polishing ; a rigidly mounted tool may be employed. The lens blank carrying device comprises a pivot pin 63 mounted in the standard 5 and carrying a member 67 in which is adjustable, by a screw 72, a rod 70 extending below the base 1 and carrying an arm 76. The arm 76- carries a rod 79 on which is angularly and axially adjustable an L-shaped bracket 82 carrying an electric motor 85 which drives through gearing 87, a pulley 88 driving through a belt 89, a shaft 91 running in ball bearings in a housing 92 on the arm 76, the shaft 91 being tapered to receive a chuck on a lens blank carrier 96. In order to effect the operative alignment between the spindle 31 and shaft 91, an arm 97 on the member 67 has secured thereto blocks 100 each carrying a screw 101 engaging a block 102 having an extension 103 projecting into an opening in the rod 70 ; by adjustment of the screws 101, the rod 70 is turned until the centre line 98 of the arm 76 is parallel to the pin 63. The arm 76, rod 70 and associated parts are swung on the axis of the pin 63 by a cam 109 held on the carrier 96 by a nut 110, a locating pin 111 on the cam fitting into a socket 112 in the carrier, so that the carrier may be removed and replaced without disturbing the relative positions of the cam 109 and the blank 113, which is held in position by screws 115. The cam is held in contact with a roller 116 by a spring 117 connected to the base 1 and to the bracket 82 so that as the carrier 96 and cam 109 rotate, the carrier is swung in accordance with the shape of the cam ; the roller 116 is carried adjustably by an arm 121 pivoted to a block 122 adjustable by a screw 126 on the base 1. The extent to which the grinding can proceed is limited by contact of the block 11 with a block 127 mounted on a support 128 on the part 5, and in order to hold the grinding tool in the raised inoperative position a latch 129 is provided pivoted to the block and adapted to be swung down to engage a notch 131 in the member 67. In the grinding of a lens, a blank B, Fig. 13, is first prepared with a central recessed circular area B<2> having the required curvature, and preferably finished and polished, an annular area B<1> around the area B<2> also being partially furnished to approximately the required curvature. The blank is then mounted on the carrier 96 in the machine described above, and the spindle 31 and shaft 91 being rotated by their motors, the tool 59 grinds the outer area B<1> and at the same time reduces the outline of the inner area B<2> to non circular form, for example, as shown at C<2> in Fig. 19, with an approximately semicircular lower edge C<3> merging into the outer'area C<1> and an upper edge C<4> or shoulder of flat arcuate form ; weights may if required be placed on the pin 36 during grinding. In a modification the lens blank carrier rotates on a fixed axis and the grinding-tool is swung, by the cam, about the axis of the pin 21. In order to form the shoulder C<4> on the area C<2> at some part thereof other than, as shown, along the flat edge, the lens blank carrier is made in two parts consisting of a main part carrying the cam and a cradle carrying the blank and pivoted to the main part so as to be adjustable by screws, and the cam is rotatably adjustable on the main part so that the shoulder may be formed where desired. After grinding and polishing, the blank is cut to the desired shape of outline.